Transfer layer repair process for attenuated masks

ABSTRACT

A method and apparatus for repairing transparent defects in a transfer layer circuit pattern in the process of fabricating an attenuated mask is provided comprising forming a sacrificial removable layer on the transfer layer including the part of the transfer layer having a transparent defect and then forming a patch to cover the transparent defect. After applying the sacrificial removable layer and patch, the sacrificial removable layer and unwanted exposed attenuated mask material is removed leaving the patch having an undercoating of sacrificial removable layer in the transparent defect region. The undercoat sacrificial removable layer is then at least partially etched and the patch and sacrificial layer removed by a lift off procedure. The transfer layer is then removed leaving the attenuated mask having the desired circuit pattern on the surface of the transparent mask substrate. Attenuated masks made using the method and apparatus of the invention are also provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method and apparatus for repairingdefects in photomasks generally used in the manufacture of semiconductormicrocircuits and other electronic components to transfer a circuitpattern onto a workpiece, and, in particular, to repairing transparentdefects in the process of making an attenuated mask using a transferlayer step. The defects are in the form of pin holes or entire missingportions in the transfer layer mask pattern which defects aretransferred to the attenuated mask and eventually to the electroniccomponent substrate during use of the attenuated mask.

[0003] 2. 2. Description of Related Art

[0004] In the manufacture of circuit patterns on electronic componentssuch as the manufacture of integrated circuits on semiconductorsubstrates, photomasks are used to transfer the desired circuit patternonto the substrate workpiece. A typical conventional photomask comprisesa patterned metal film such as chromium, nickel or aluminum in athickness of about 1000 Å deposited on a transparent base such as glassor quartz. The photomask is generally manufactured by depositing a thinlayer of the metal on the surface of the transparent substrate, coatingthe film metal with a photoresist, exposing the desired pattern on thephotoresist coating, developing the photoresist coating, and removingthe metal from the developed areas of the film by etching then removingthe remaining photoresist leaving a patterned metal film on thesubstrate.

[0005] The pattern contained in the photomask is reproduced onto thesurface of the workpiece typically by placing the mask over theworkpiece and irritating a radiation-sensitive resist material on theworkpiece. The variety of radiation sources include visible light,ultraviolet light, x-ray radiation, electrons and ions. When illuminatedby the radiation, the metal pattern on the photomask serves toselectively block portions of the radiation beam while allowing otherportions to be transmitted through the non-metallized areas. In thisprocedure, complex geometry having very narrow line widths can bereproduced allowing an economical production of very large scaleintegrated circuits and other electronic devices.

[0006] The type of mask to which this invention is particularly directedis an attenuated mask which is built using a transfer layer of chromethat allows the chrome to act as a mask to the attenuated film under thechrome layer. The transfer layer of chrome is generally patterned asnoted above with the difference being that the chrome will eventually beremoved exposing a pattern of attenuated material under the chromeforming the desired attenuated mask circuit pattern.

[0007] To make an attenuated mask, an attenuation layer is formed on asubstrate such as glass or quartz by coating a layer of an attenuatingmaterial such as molybdenum silicide (MoSi) on the substrate surface. Achrome transfer layer is then applied over the attenuated materialcoating and is patterned as discussed above to form the desired chromepattern and ultimately the desired attenuated material pattern which isunder the chrome pattern on the substrate surface.

[0008] If there are defects in the chrome pattern such as missing chromethese are termed transparent defects and can take the form of pinholesor entire missing portions of the chrome film. Such defects in thechrome are also transferred to the attenuation material and to the maskduring the development step. This is a serious problem since matching ofthe phase and transmission properties of the attenuater material iscurrently impossible.

[0009] To eliminate the transfer of the transparent defects into theattenuated film, a repair is generated that is resistant to the etch ofthe final attenuated film such as a plasma etch. This is typicallyaccomplished using a FIB patch made primarily of gold and carbon. Thismaterial is inert to the etch used to remove the attenuated maskmaterial such as MoSi. Unfortunately, the patch is also inert when thechrome is to be etched so that when the chrome is removed from the mask,the gold and carbon patch material remains because of the inability ofthe chrome etch to attack the patch material. With such residual orremaining patches on the mask, the attenuated film properties areeffected and cause printed defects on the wafer substrate when imagedusing the attenuated mask.

[0010] A number of patents have issued in the area of repairingdefective conventional chrome photomasks and include U.S. Pat. Nos.4,340,654; 4,510,222; 4,636,403; 4,778,693; 4,874,632; 5,011,580; and5,273,849. These patents discuss the various types of conventionalphotomasks and the different methods employed to repair transparent typedefects on the photomasks and the disclosures of each of the abovepatents are hereby incorporated by reference.

[0011] The following description will be directed to the repair ofattenuated phase shift masks which may be made using a variety ofattenuating materials such as MoSi, carbon and silicon nitride but itwill be appreciated by those skilled in the art that the inventionapplies to other masks where repair of transparent defects is needed.

[0012] Bearing in mind the problems and deficiencies of the prior art,it is therefore an object of the present invention to provide a methodto repair transparent defects in the fabrication process for makingattenuated masks which are used to make electronic components such assemiconductors.

[0013] It is another object of the present invention to provide anapparatus to repair transparent defects in the fabrication process formaking attenuated photomasks used to make semiconductors and otherelectronic components.

[0014] A further object of the invention is to provide attenuatedphotomasks made in accordance with the method and apparatus of theinvention.

[0015] Other advantages of the invention will be readily apparent fromthe following description.

SUMMARY OF THE INVENTION

[0016] The above and other objects and advantages, which will beapparent to one of skill in the art, are achieved in the presentinvention which is directed, in a first aspect,to a method of formingdefect free mask transfer layers comprising the steps of:

[0017] a) forming image segments in a mask transfer layer on asubstrate;

[0018] b) inspecting the substrate for defects;

[0019] c) repairing the defects; and

[0020] d) removing the mask transfer layer.

[0021] In another aspect a transfer layer fabrication method is providedfor making an attenuated mask which requires a repair step to repairtransparent defects in the transfer layer comprising the steps of:

[0022] supplying a transparent mask substrate;

[0023] depositing a layer of attenuated mask material on the masksubstrate;

[0024] forming a metallic transfer layer on the attenuated mask materiallayer in a desired mask pattern leaving unwanted attenuated maskmaterial exposed;

[0025] inspecting the metallic layer for transparent defects whereinmetal is missing from the desired transfer layer design leaving wantedattenuated mask material exposed and forming transparent defects;

[0026] applying a sacrificial removable layer on the metallic transferlayer and wanted and unwanted attenuated mask material;

[0027] applying a patch material on top of the sacrificial removablelayer in the transparent defect missing portion of the metallic transferlayer;

[0028] etching the sacrificial removable layer and unwanted exposedattenuated mask material;

[0029] contacting the etched substrate with an etchant which undercutsthe patch material and at least partially etches the sacrificialremovable layer under the patch material;

[0030] removing the patch material and remaining sacrificial removablelayer; and

[0031] etching the metallic layer forming the attenuated mask whichcomprises the attenuated mask material in the form of the desiredcircuit pattern on the transparent mask substrate.

[0032] In a further aspect of the invention, a method is provided forrepairing transparent defects in a transfer layer, typically metal, inthe process for making attenuated masks using a transfer layer whichcovers wanted attenuated mask material leaving unwanted attenuated maskmaterial exposed wherein the attenuated mask comprises a circuit patternof an attenuated mask material (in either a negative or positive form),on a transparent mask substrate which attenuated mask pattern istransferred to an electronic component substrate the method comprisingthe steps of:

[0033] inspecting the metallic layer for transparent defects whereinmetal is missing from the desired transfer layer design leaving wantedattenuated mask material exposed and forming transparent defects;

[0034] applying a sacrificial removable layer on the transfer layer andwanted and unwanted attenuated mask material;

[0035] applying a patch material on top of the sacrificial removablelayer in the transparent defect missing portion of the metallic transferlayer;

[0036] etching the sacrificial removable layer and unwanted exposedattenuated mask material;

[0037] contacting the etched substrate with an etchant which undercutsthe patch material and at least partially etches the sacrificialremovable layer under the patch material;

[0038] removing the patch material and remaining sacrificial removablelayer; and

[0039] etching the metallic layer forming the attenuated mask whichcomprises the attenuated mask material in the form of the desiredcircuit pattern on the transparent mask substrate.

[0040] In another aspect of the invention, an apparatus is provided forrepairing transparent defects in a transfer layer in the process ofmaking attenuated masks made using a transfer layer process wherein theattenuated mask has a circuit pattern of an attenuated mask materialthereon which pattern is transferred to an electronic componentsubstrate comprising:

[0041] holding means for securing an attenuated mask substrate having acircuit pattern thereon in the form of a transfer layer on an attenuatedmask material on a transparent mask substrate, the transfer layer beingin the desired mask pattern covering wanted attenuated mask materialleaving unwanted attenuated mask material exposed;

[0042] detecting means for locating and identifying a transparent defectin the transfer layer exposing wanted attenuated mask material;

[0043] application means to form a sacrificial removable layer on thetransfer layer and exposed wanted and unwanted attenuated mask material;

[0044] application means for applying a patch material on top of thesacrificial removable layer in the transparent defect missing portion ofthe transfer layer;

[0045] a first etching means to etch the sacrificial removable layer andunwanted exposed attenuated mask material;

[0046] a second etching means for etching the etched substrate to removeat least some of the sacrificial removable layer under the patchmaterial;

[0047] removing means for removing the patch material and any remainingsacrificial removable layer under the patch material; and

[0048] a third etching means for etching the transfer layer forming theattenuated mask in the form of attenuated mask material in the desiredmask pattern on the transparent mask substrate.

[0049] Attenuated masks made by the method and apparatus of theinvention are also provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The features of the invention believed to be novel and theelements characteristic of the invention are set forth withparticularity in the appended claims. The figures are for illustrationpurposes only and are not drawn to scale. The invention itself, however,both as to organization and method of operation, may best be understoodby reference to the detailed description which follows taken inconjunction with the accompanying drawings in which:

[0051]FIG. 1 is a top plan view of a chrome transfer layer needingrepair which layer is on a film of attenuated mask material.

[0052]FIG. 2 is a cross-sectional side view of FIG. 1 taken along lines2-2.

[0053]FIG. 3 is a cross-sectional side view of FIG. 1 taken along lines3-3 and showing a transparent defect in the chrome transfer layer.

[0054]FIG. 4 is a cross-sectional side view taken along lines 4-4 ofFIG. 1 showing a pinpoint transparent defect in the chrome transferlayer.

[0055] FIGS. 5A-5F show, in sequence, the method of the invention forrepairing transparent defects in a transfer layer in the fabrication ofan attenuated mask.

[0056] FIGS. 6A-6E show the conventional method of making a attenuatedmask using a metallic transfer layer.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0057] In describing the preferred embodiments of the present invention,reference will be made herein to FIGS. 1-6E of the drawings in whichlike numerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

[0058] The present invention is used to repair transparent defects inphotomasks and any type photomask may be repaired using the method andapparatus of the invention. For convenience, however, the followingdescription will be directed to attenuater material on quartz photomasks(attenuater photomasks) which are made using a metallic transfer layerto form the desired attenuater design on the quartz transparentsubstrate.

[0059] Attenuated masks typically comprise an attenuating mask materialsuch as molybdenum silicide (MoSi) to form the attenuating design on thequartz, glass or other transparent substrate. The silicide film istypically the order of about 1000 Å. Also for convenience, the followingdescription will be directed to the repair of patterns in the form ofparallel conductor lines but it will be appreciated by those skilled inthe art that other type patterns (e.g., pads) may likewise be repairedusing the method and apparatus of the invention.

[0060] Basically, the invention comprises a method for repairing atransparent defect in a transfer layer used during the fabricationprocess for making an attenuated mask. An inspection technique isemployed to determine the location of transparent defects in thetransfer layer and a sacrificial layer of metal is then applied to thecomplete substrate surface including the transfer layer, wantedattenuater material exposed by the defect and unwanted exposedattenuater material. A patch is then applied to cover the transparentdefect. The exposed sacrificial metal layer and the unwanted exposedMoSi layer is then removed leaving the transfer layer, patch and thesacrificial layer under the patch and on top of the wanted attenuatedmaterial. The sacrificial layer under the patch is then at leastpartially etched and the patch and sacrificial layer removed. Thetransfer layer is then removed leaving the desired attenuating materialon the transparent substrate in the desired circuit pattern.

[0061] Referring first to FIGS. 6A-6E these figures show, in sequence, aconventional method for making an attenuated mask. In FIG. 6A thequartz, glass, or other transparent substrate 11 is overlaid with acoating 12 of an attenuating material such as MoSi, carbon and siliconnitride. MoSi is a preferred attenuating material and the followingdescription will be directed to this material for convenience. Thethickness of the MoSi layer is typically about 600 to 1500 Å.

[0062] In FIG. 6B, a transfer layer 13 is applied on top of the MoSilayer 12. The transfer layer is typically a metallic material such aschrome and is applied at a thickness typically about 500 to 1500 Å. Thefunction of the metallic layer is to form the desired circuit patternand allow etching of the unwanted attenuated material on the substratesurface.

[0063] The metallic transfer layer 13 is patterned into the desiredattenuated mask circuit pattern as shown in FIG. 6C. The metallictransfer layer 13 is shown in the form of parallel conductor linesalthough other shapes such as pads, straps, etc. may be patterned andrepaired using the method and apparatus of the invention.

[0064] The exposed unwanted MoSi layer 12 a is then etched leaving aMoSi layer 12 covered by the chrome pattern 13 as shown in FIG. 6D. Thechrome pattern transfer layer is then removed leaving the desiredattenuating mask shown generally as 18 in FIG. 6E. Accordingly, thefinal attenuated mask comprises a transparent substrate 11 having MoSipattern features 12 on the surface thereof.

[0065] Referring now to FIG. 1, chrome or other metal transfer layerlines 13 are shown on the surface of attenuating material 12. Thisconfiguration shown generally as 10 represents a chrome transfer layerneeding repair in the fabrication of an attenuated mask. Accordingly,the chrome lines 13 are shown having a transparent defect 14 whereinpart of the chrome line is missing and a transparent defect 15 wherein apinhole or other opening in the chrome line is missing.

[0066] A cross-sectional side view of FIG. 1 is shown in FIG. 2 whereinthe metallic transfer layer 13 in the desired circuit pattern is formedon the surface of the attenuating material layer 12 which is on top ofthe transparent layer 11. There are no transparent defects shown in thiscross-section.

[0067] In FIG. 3, the transparent defect 14 is shown in the metallictransfer layer 13. Likewise, in FIG. 4 the pinhole transparent defect 15is shown in metallic transfer layer 13. It is the defects shown in FIG.3 and 4 which need to be repaired before the desired attenuated mask canbe completed.

[0068] Referring now to FIGS. 5A-5F, a sequence of steps is shown torepair a transfer layer in the transfer layer process of making anattenuated mask using the method of the invention. In FIG. 5A a quartzsubstrate 11 is shown covered with a coating of an attenuating material12 which is covered with a patterned transfer metallic layer 13 shownhaving a defect 14 and an edge 14 a. The device shown in FIG. 5A isdesignated generally as 10 and is similar to the design shown in FIGS. 1and 3.

[0069] The structure in FIG. 5A is overcoated with a sacrificialremovable layer 16 using a material such as copper. The copper may bedeposited by a variety of conventional means such as evaporation,sputtering and usually to a thickness of about 25 Å to 150 Å. Greaterthicknesses can be used but may effect placement of final images andoveretch of the MoSi. It will be seen that the sacrificial layer 16covers the transfer layer 13, the sides of the transparent defect 14,edge of the defect 14 a and the attenuating material 12.

[0070] A patch material 17 is then applied to the defect and typicallyoverlays part of the transfer layer 13 shown as 13 a. It will be seenthat the patch covers the transparent defect out to its outer edge 14 athereby covering the wanted MoSi layer 12 to its desired design.

[0071] The sacrificial removable layer 16 and the unwanted MoSi layer 12are then removed by etching with the resulting etched substrate shown inFIG. 5D. This leaves the desired MoSi design 12 covered by the transferlayer 13 and the patch 17 having an undercoating of the sacrificialremovable layer 16.

[0072] The sacrificial removable layer 16 under the patch is then atleast partially etched using a solvent such as dilute nitric acid, e.g.,10%, and the undercoat sacrificial layer 16 and patch 17 removed by aliftoff procedure. The etching is typically performed by immersion ofthe substrate in the etchant. After the liftoff procedure, the structureis shown as in FIG. 5E and comprises the transparent substrate 11 andthe MoSi patterned layer 12 covered by the metallic chrome transferlayer 13. The transparent defect is still present as 14. Upon etching ofthe chrome layer 13 the desired attenuated mask 18 is formed as shown inFIG. 5F.

[0073] Referring back to FIG. 5C, in the application of the patch to thestructure, any repair method may be used which provides a patch whichcovers the transparent defect. Any suitable patch material may be usedsuch as gold and carbon and it may be applied by any of a number oftechniques or a deposition technique using a focus ion beam.

[0074] A preferred method of applying a patch is by using a focus ionbeam (FIB) and is a preferred method of applying the patch. Generally,an organo metallic gas such as dimethylgold trifluoro acetylacetonate isused and the gas is discharged from a gas nozzle and the gas supplied inthe vicinity of the defect such as 14 shown in FIG. 1. The defectportion 14 is radiated by the ion beam simultaneously decomposing thegas and the metal. Carbon which is a component of the gas and the metalselectively forms a patch in the defect portion. This repair method isfound to be simple and has a high repair resolution of about ±0.1microns making it an extremely effective means for repairing the defectsin a pattern.

[0075] A preferred patch material is dimethylgold trifluoroacetylacetonate which when decomposed by the FIB provides a gold/carbonpatch. The patch preferably overlays part of the transfer layer at thetransparent defect as shown in FIG. 5D.

[0076] While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

[0077] Thus, having described the invention, what is claimed is:

1. A method of forming defect free mask transfer layers comprising thesteps of: forming image segments in a mask transfer layer on asubstrate; inspecting the substrate for defects; repairing the defects;and removing the mask transfer layer.
 2. A transfer layer fabricationmethod for making an attenuated mask which requires a repair step torepair transparent defects in the transfer layer comprising the stepsof: supplying a transparent mask substrate; depositing a layer ofattenuated mask material on the mask substrate; forming a metallictransfer layer on the attenuated mask material layer in a desired maskpattern leaving unwanted attenuated mask material exposed; inspectingthe metallic layer for transparent defects wherein metal is missing fromthe desired transfer layer design leaving wanted attenuated maskmaterial exposed and forming transparent defects; applying a sacrificialremovable layer on the metallic transfer layer and wanted and unwantedattenuated mask material; applying a patch material on top of thesacrificial removable layer in the transparent defect missing portion ofthe metallic transfer layer; etching the sacrificial removable layer andunwanted exposed attenuated mask material; contacting the etchedsubstrate with an etchant which undercuts the patch material and atleast partially etches the sacrificial removable layer under the patchmaterial; removing the patch material and remaining sacrificialremovable layer; and etching the metallic layer forming the attenuatedmask which comprises the attenuated mask material in the form of thedesired circuit pattern on the transparent mask substrate.
 3. The methodof claim 2 wherein the attenuated mask material is MoSi.
 4. The methodof claim 2 wherein the metallic transfer layer is chrome.
 5. The methodof claim 2 wherein the sacrificial removable layer is copper.
 6. Amethod for repairing transparent defects in a metal transfer layer inthe process for making attenuated masks using a transfer layer whichcovers wanted attenuated mask material leaving unwanted attenuated maskmaterial exposed wherein the attenuated mask comprises a circuit patternof an attenuated mask material in either a negative or positive form ona transparent mask substrate which attenuated mask pattern istransferred to an electronic component substrate the method comprisingthe steps of: inspecting the metallic layer for transparent defectswherein metal is missing from the desired transfer layer design leavingwanted attenuated mask material exposed and forming transparent defects;applying a sacrificial removable layer on the metallic transfer layerand wanted and unwanted attenuated mask material; applying a patchmaterial on top of the sacrificial removable layer in the transparentdefect missing portion of the metallic transfer layer; etching thesacrificial removable layer and unwanted exposed attenuated maskmaterial; contacting the etched substrate with an etchant whichundercuts the patch material and at least partially etches thesacrificial removable layer under the patch material; removing the patchmaterial and remaining sacrificial removable layer; and etching themetallic layer forming the attenuated mask which comprises theattenuated mask material in the form of the desired circuit pattern onthe transparent mask substrate.
 7. The method of claim 6 wherein theattenuated mask material is MoSi.
 8. The method of claim 6 wherein themetallic transfer layer is chrome.
 9. The method of claim 6 wherein thesacrificial removable layer is copper.
 10. The method of claim 9 whereinthe etchant for undercutting the patch material is nitric acid.
 11. Anapparatus for repairing transparent defects in a transfer layer in theprocess of making attenuated masks made using a transfer layer processwherein the attenuated mask has a circuit pattern of an attenuated maskmaterial thereon which pattern is transferred to an electronic componentsubstrate comprising: holding means for securing an attenuated masksubstrate having a circuit pattern thereon in the form of a transferlayer on an attenuated mask material on a transparent mask substrate,the transfer layer being in the desired mask pattern covering wantedattenuated mask material leaving unwanted attenuated mask materialexposed; detecting means for locating and identifying a transparentdefect in the transfer layer exposing wanted attenuated mask material;application means to form a sacrificial removable layer on the transferlayer and exposed wanted and unwanted attenuated mask material;application means for applying a patch material on top of thesacrificial removable layer in the transparent defect missing portion ofthe transfer layer; a first etching means to etch the sacrificialremovable layer and unwanted exposed attenuated mask material; a secondetching means for etching the etched substrate to remove at least someof the sacrificial removable layer under the patch material; removingmeans for removing the patch material and any remaining sacrificialremovable layer under the patch material; and a third etching means foretching the transfer layer forming the attenuated mask in the form ofattenuated mask material in the desired mask pattern on the transparentmask substrate.
 12. The apparatus of claim 11 wherein the applicationmeans is a focused ion beam.
 13. The apparatus of claim 11 wherein thesecond etching means is nitric acid and the sacrificial removable layeris copper.
 14. An attenuated mask made using the method of claim 1 . 15.An attenuated mask made using the method of claim 2 .
 16. An attenuatedmask made using the method of claim 3 .
 17. An attenuated mask madeusing the method of claim 4 .